Redundant role of TLR9 for anti-Candida host defense

The role of Toll-like receptor-9 (TLR9) in the recognition of Candida albicans and anti-Candida host defense was investigated in a murine model of disseminated candidiasis and in human peripheral blood mononuclear cells (PBMC). Blocking TLR9 by a specific inhibitor of human TLR9 or stimulation of cells isolated from TLR9-deficient (TLR9−/−) mice resulted in a 20–30% reduction in cytokine production induced by C. albicans. However, this defect was not accompanied by differences in mortality and organ fungal growth between TLR9−/− and TLR9+/+ mice. In conclusion, TLR9 is a pathogen-recognition receptor for C. albicans, and TLR9 is involved in the induction of cytokines in response to C. albicans. However, the cytokine defect in TLR9−/− mice is compensated by alternative pathways, and the TLR9-dependent pathway seems to be redundant in the disseminated candidiasis model in mice.